VoIP, or Voice over IP, simply means voice data that is tranferred over the internet. The next time you're shooting the breeze on Viber, Skype or Google Hangouts on your phone, keep in mind that Airtel will charge you you even if you're already paying for that data.

Airtel's move flies in the face of net neutrality, which is a hot topic round the globe. In the United States, for instance, there is a proposal to provide "fast lanes" for data intensive video-streaming services like Netflix and Hulu. Simply put, internet services providers want to charge these companies extra for carrying their bits to the consumer, even though the consumers are already paying the service providers for internet access in the first place. Last month, President Barack Obama came out strongly in support of net neutrality by saying that "a free and open internet was as critical to Americans' lives as electricity and telephone service and should be regulated like those utilities to protect consumers."

The timing of this move isn't surprising. Whatsapp, which has wiped off a large part of SMS revenues for mobile service providers in India, has long been rumoured to introduce voice-calling over data. Indians already pay some of the lowest rates in the world for voice calls and carriers like Airtel are afraid that once people start using data to make voice calls, these revenues will be wiped out as well.

Indeed, in August, the Telecom Regulation Authority of India (TRAI) had quashed a proposal from Indian telecom companies to charge over-the-top players like Whatsapp and Viber extra "connectivity charges." TRAI stated that telcos could make up for the lost revenue with the increase in mobile data usage.

In a statement to Hindustan Times, an Airtel spokesperson said: "We have made some revisions in the composition of our data packs, and will offer VoIP (Voice over internet protocol) connectivity through an independent pack that will be launched shortly. Our customers can continue enjoying voice calls over data connectivity by opting for this VoIP pack, or simply use VoIP services on pay-as-you-go basis."

Which basically means this: unless you buy a seperate VoIP pack, you'll be charged extra for making calls using Skype, Viber and other services. If you don't think net neutrality is something to lose sleep over yet, think about this: If it's VoIP today, operators might start charging you extra to stream YouTube or use a music service like Saavn tomorrow. It is not immediately clear if other operators will follow Airtel's move.